When a work is polished, generally, the polishing is carried out by pressing the work against a polishing pad adhered to a turn table while polishing slurry is flowed on the polishing pad and by rotating the work and the turn table.
A polishing apparatus used for the polishing has a turn table to which a polishing pad is adhered, a turn table receiving member having grooves and supporting the turn table by a grooved surface, a polishing slurry supplying means for supplying polishing slurry to the polishing pad, and a rotating means for rotating a work and the turn table.
Recently, for improving productivity, concretely, for reducing a time of apparatus stop when polishing pads are exchanged, a polishing apparatus in which a turn table is detachable has been used. With the polishing apparatus, while casting, stainless steel and ceramic having high strength are used for materials of the turn table and the turn table receiving member for heightening hardness of the polishing apparatus, grooves are formed in a turn table support surface of the turn table receiving member for easily detaching the turn table from the turn table receiving member.
However, during polishing with the polishing apparatus, the turn table receives a polishing load from the work, while the turn table receives a reaction force from the turn table receiving member. The reaction force becomes contact pressure between the polishing pad and the work. In this case, if grooves are formed in the turn table receiving member, thereby the turn table receives the reaction force from non-groove portions of the turn table receiving member, but does not receive the reaction force from grooved portions. As a result, the contact pressure between the polishing pad and the work becomes non-uniform within a surface of the work, thereby a polishing rate of the work becomes non-uniform within the surface to form minute waviness on the work surface.
With the preceding developed art, as shown in FIG. 6, for example, in a case that concentric circle-like grooves 9d are provided in a turn table receiving member 3d and that a rotation center of the turn table receiving member 3d and a rotation center of a work coincide with each other, strong portions and weak portions of contact pressure against a polishing pad generate concentrically and alternately about the rotation center of the work. In this case, the polishing rate of the work changes according to the contact pressure. Thus, with the work, portions corresponding to the non-groove portions are more polished, while portions corresponding to the grooved portions are less polished, thereby, as shown in FIG. 8, concentric circle-like waviness is formed on the work W. That is, for example, irregularities of about not more than 0.1 .mu.m are formed periodically on the work. Such a phenomenon is observed when a pattern of the grooves 9d of the turn table receiving member 3d is concentric circle-like or spiral.
Further, even if the rotation center of the turn table receiving member and the rotation center of the work do not coincide with each other, that is, the rotation center of the work is eccentric from the rotation center of the turn table receiving member, when concentric circle-like grooves are provided in the turn table receiving member, the contact pressure to the polishing pad in the vicinity of the rotation center of the work becomes either constantly strong or constantly weak, thereby there is a problem that a polishing degree is changed between a central portion of the work and a peripheral portion thereof.
The present invention was developed in view of the above-described problems. An object of the present invention is to provide a polishing method and a polishing apparatus for making contact pressure between a work and a polishing pad substantially uniform within surfaces to obtain a work having good quality.